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Why do members of the same species share a gene pool?

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A nautilus mollusk with a spiral, brown-and-white striped shell and numerous white tentacles extending from its soft body, set against a dark background. — species A nautilus (*Nautilus*) floating in the water column of the ocean.

Members of the same species share a common gene pool because they are groups of interbreeding natural populations that are reproductively isolated from other such groups.1

The ability to interbreed is the fundamental mechanism that maintains this shared genetic resource. Through interbreeding, genetic material is exchanged between individuals, a process known as gene flow. This exchange ensures that genetic changes—which originate in single individuals—can spread throughout the population. Because members of a species can reproduce with one another, they function as independent evolutionary units, collectively maintaining a set of genes and alleles that is distinct from the gene pools of other species.213

If gene flow is interrupted, populations may begin to diverge genetically, eventually leading to the formation of separate species as their respective gene pools become disharmonious and they lose the ability to interbreed.41